1. Field of the Invention
The present invention relates to a photographic processing apparatus, and, more particularly, to a photographic material processing apparatus for processing a continuous web of photographic material. The apparatus has a simplified structure to enable efficient supply of a replenishing solution to a processing tank.
2. Description of Related Art
Typically, photographic material wet processing, including development, bleach, fixation and stabilization, is accompanied by replenishment of a fresh processing solution mixed with auxiliary developer agents. In order to produce pictures of uniform quality, photographic materials are immersed in plenty of processing solution. While using large quantities of processing solution is advantageous in producing uniform quality pictures, various constraints should be imposed to keep the desired chemical characteristics of the processing solution. For instance, if only a small quantity of photographic material is processed in a large amount of processing solution, the processing solution is apt: 1) to be oxidized with air, 2) to have the chemical characteristics of its components deteriorate due to absorption of carbonic acid gas and/or 3) to lower its pH value, each of which can result in poor quality pictures. In view of the demands of controlling the chemical characteristics of the processing solution, reducing resources and maintaining the environment, it is desired to use the smallest quantities of processing and replenishing solutions as possible.
To meet these demands, use of a processing apparatus having a processing tank and a processing rack has been effective. This type of processing tank and rack are configured so as to form a small volume therebetween for holding a processing solution.
For the purpose of providing a brief background of this type of photographic processing apparatus to enhance understanding of the operation of a photographic processing apparatus according to the present invention, reference is made to FIG. 4 showing a prior art photographic paper processing or developing apparatus. As FIG. 4 shows, the photographic paper processing apparatus 100 is equipped with a processing solution circulation system 200 for circulating the processing solution through a processing tank 101 while processing photographic paper. The processing solution circulation system 200 includes a pump 205 to force the processing solution out from and into the processing tank 101 through a circulation conduit 204 extending between an inlet nozzle 102 and an outlet nozzle 103 of the processing tank 101. As the apparatus develops a large amount of photographic paper, the processing solution is gradually consumed and the processing solution's chemical performance deteriorates. To correct this chemical change, supply of the fresh processing solution including auxiliary developer agents, which are collectively referred to as a replenisher solution, or simply replenisher, is supplementarily compelled.
Supply of fresh replenisher through the circulation conduit 204 maintains a fresh and uniform quality processing solution, however, there are various structural constraints which must be imposed on the circulation system 200 for proper operation. In the prior art photographic paper processing apparatus 100, the processing tank 101 must be connected with both ends of the inlet and circulation conduit 204 (having a small drift space or cross-sectional area), at both the spout nozzle 102 and the discharge or outlet nozzle 103. This structure causes, on one hand, a sharp decrease in resistance in the processing solution being discharged into the circulation conduit 204 through the discharge nozzle 103 and, on the other hand, a sharp increase in resistance in the processing solution entering the spout nozzle 102 from the circulation conduit 204. These changes in resistance result in pressure fluctuations of the developing solution in the circulation conduit 204 which directly effect the liquid level of the replenisher in the replenisher tank 300. Accordingly, in order to handle the pressure differences, the circulation system 200 is not in any way allowed to be left open to air to make up for lost replenisher.
In place of providing an access opening in the circulation conduit 204, a pump 206 is incorporated in the circulation system 200 so as to force replenisher supply to the circulation conduit 204 through a filtering case. For the purpose of supplying replenisher, there is a strong demand for high performance pumps, such as a plunger type and a diaphragm type, both of which have high pressure discharging performance. These types of pumps are always relatively expensive as compared to a bellows pumps. A bellows pump, which is simple in structure and relatively inexpensive, is unsuitable for the circulation system 200 since it can not supply replenisher at a high pressure level.
Further, in order to reduce the pressure difference of the developing solution with respect to the atmospheric pressure caused due to resistance at the spout nozzle 102 and discharge nozzle 103, an orifice can be incorporated in the circulation conduit 204. The orifice allows the circulation conduit 204 to be open to air on either the upstream side or the downstream side from the orifice. Thus, replenisher can be supplied to the circulation conduit 204 through the opening. This configuration, however, causes an indispensable problem in that a restricted flow rate at the nozzles significantly aggravates the efficiency of the development of the photographic material.
Another prior art photographic processing apparatus intended to use only small quantities of processing solution and replenisher is disclosed in U.S. Pat. No. 5,270,762. The approach in reducing the quantity of processing solution used in U.S. Pat. No. 5,270,762 is to dimension a processing tank and a processing rack so as to form a small volume for holding the processing solution and photographic material. This structure allows use of a reduced quantity of processing solution and results in suppressing evaporation and deterioration or oxidization of processing solution. The photographic processing apparatuses of this type have the further advantage of miniaturization and simplification of the processing assembly.
In many instances where a processing tank and a processing rack are configured and assembled so as to form a small volume therebetween for holding a processing solution, it is still necessary to make up for the loss of processing solution through a replenishing system. Because of a small volume of processing solution servicing in the processing tank, the processing solution is concentrated in the processing tank in close proximity to the inlet due to the supply of fresh replenisher and becomes less in concentration in the processing tank in close proximity to the outlet as the result of deterioration of the processing solution. Further, while the processing solution has strong activity around the inlet, it is less agitated, resulting in an overall inferior mixture of the servicing processing solution and fresh processing solution within the processing tank. In other words, this type of processing tank assembly has the disadvantage of nonhomogeneous distribution of the concentration of processing solution in the processing tank, which can produce developing stain, developing marks and nonuniform picture quality.